Each day, thousands of pieces of intelligence information from around
the world -- field reports, captured documents, news from foreign
allies and sometimes idle gossip -- arrive in a computer-filled
office in McLean, where analysts feed them into the nation's central
list of terrorists and terrorism suspects.

Called TIDE, for Terrorist Identities Datamart Environment, the list
is a storehouse for data about individuals that the intelligence
community believes might harm the United States. It is the wellspring
for watch lists distributed to airlines, law enforcement, border
posts and U.S. consulates, created to close one of the key
intelligence gaps revealed after Sept. 11, 2001: the failure of
federal agencies to share what they knew about al-Qaeda operatives.

But in addressing one problem, TIDE has spawned others. Ballooning
from fewer than 100,000 files in 2003 to about 435,000, the growing
database threatens to overwhelm the people who manage it. "The single
biggest worry that I have is long-term quality control," said Russ
Travers, in charge of TIDE at the National Counterterrorism Center in
McLean. "Where am I going to be, where is my successor going to be,
five years down the road?"

TIDE has also created concerns about secrecy, errors and privacy. The
list marks the first time foreigners and U.S. citizens are combined
in an intelligence database. The bar for inclusion is low, and once
someone is on the list, it is virtually impossible to get off it. At
any stage, the process can lead to "horror stories" of mixed-up names
and unconfirmed information, Travers acknowledged.

The watch lists fed by TIDE, used to monitor everyone entering the
country or having even a casual encounter with federal, state and
local law enforcement, have a higher bar. But they have become a
source of irritation -- and potentially more serious consequences --
for many U.S. citizens and visitors.

In 2004 and 2005, misidentifications accounted for about half of the
tens of thousands of times a traveler's name triggered a watch-list
hit, the Government Accountability Office reported in September.
Congressional committees have criticized the process, some charging
that it collects too much information about Americans, others saying
it is ineffective against terrorists. Civil rights and privacy groups
have called for increased transparency.